Phosphate-promoted nickel catalyst for high temperature oligomerization

ABSTRACT

An oligomerization catalyst, oligomer products, methods for making and using same. The catalyst can include a supported nickel phosphate compound. The catalyst is stable at oligomerization temperatures of 500° C. or higher and particularly useful for making oligomer products containing C4 to C26 olefins having a boiling point in the range of 170° C. to 360° C.

CROSS REFERENCE TO RELATED APPLICATIONS

The current application is a Divisional and claims the benefit ofco-pending U.S. patent application Ser. No. 16/362,132 filed on Mar. 22,2019, entitled “PHOSPHATE-PROMOTED NICKEL CATALYST FOR HIGH TEMPERATUREOLIGOMERIZATION.” This reference is hereby incorporated in its entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under CooperativeAgreement No. EEC-1647722 awarded by the National Science Foundation.The government has certain rights in the invention.

BACKGROUND Field of the Invention

Embodiments of the present invention generally relate to lighthydrocarbon alkene oligomerization. More particularly, embodimentsrelate to new catalyst for light hydrocarbon alkene oligomerization.

Description of the Related Art

Oligomerization is a process by which short chain olefin monomers areconverted to intermediate chain-length olefins having relatively fewermonomers as compared to polymerization where the number of monomers inthe chain is high resulting in high molecular weight products, polymers.Such conversion of shorter chain olefins (formed from steam cracking,Fluid Catalytic Cracking, Fischer-Tropsch processes, etc.) to longerchain hydrocarbons has been of considerable interest in the past.Gasoline/motor fuel, for example, has been produced by theoligomerization of olefins in cracked refinery gas since the early1930's. The petrochemical industry also utilizes ethyleneoligomerization for production of linear higher carbon α-olefins to beused for detergents, plasticizers, and a variety of industrialchemicals.

Conventional processes for ethylene oligomerization utilizinghomogeneous catalysts have been based on nickel (Ni), titanium (Ti),zirconium (Zr), and chromium (Cr) complexes. These homogeneous catalystsshow high activity, good control of chain length and preferentialformation of linear alpha olefins. One example of such process forconverting ethylene to high carbon olefins is the Shell Higher OlefinsProcess (SHOP) that was developed by Wilhelm Keim. The SHOP is catalyzedby a Ni complex bearing a chelating ligand with a neutral phosphine andan anionic oxygen donor. Another example is a titanium chloride catalystin combination with aluminum ethyl chloride Al(C₂H₅)₂Cl that wasdiscovered by Karl Ziegler and Heinz Martin and used to catalyze theconversion of ethylene to 1-butene with high selectivity. This has beencommonly known as the Ziegler catalyst.

Various modifications of the Ziegler catalyst have been developed overthe years. Chauvin et al., for example, developed the Alphabutol processfor 1-butene production from ethylene with a titanium catalyst, whichcan achieve a Turnover Frequency (TOF) approaching 106 h⁻¹. Zirconiumalkoxides display a lower activity but a comparable selectivity forconverting ethylene to 1-butene. The Chevron Phillips (Gulfene) andIneos (Ethlyl) processes used an aluminum Zeigler catalyst forconverting ethylene to 1-butene. ldemitsu Kosan Co. Ltd. developedzirconium (IV) complex for oligomerization. IFP Energies nouvelles(IFPEN) and SABIC-Linde used a zirconium precursor, a ligand, and analuminum co-catalyst. Phillip's used a trimerization catalyst where theactive metal is chromium (Cr) on an amorphous support of porous silica.

After the success of nickel, titanium, zirconium and chromium, othertransition metal complexes of cobalt and iron were explored as potentialcatalysts for olefin oligomerization.

The Brookhart group and Britovsek et al., for example, studied iron (II)and cobalt (II) catalysts bearing pyridine ligands. Such catalysts,however, were sensitive to impurities in the feed, sensitive totemperature, difficult to separate from the products, and/or had lowpotential for reusability.

There is a need, therefore, for a new and improved oligomerizationcatalyst capable of oligomerization at acceptable conversion rates andovercoming the aforementioned shortcomings of predecessor catalysts foroligomerization.

SUMMARY

An oligomerization catalyst, oligomer products and methods for makingand using the same are provided. The catalyst can include a supportednickel phosphate compound and is stable at oligomerization temperaturesof 500° C. or higher. The catalyst is particularly useful for makingoligomers containing C4 to C26 olefins having a boiling point in therange of 170° C. to 360° C., which can be used to produce diesel and jetfuels.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 shows a XANES spectra of an inventive Ni—P/SiO₂ catalyst providedin the Example below.

FIG. 2 shows a XANES spectra of a comparative Ni/SiO₂ catalyst providedin the Example below.

FIG. 3 shows an EXAFS spectra of the inventive Ni—P/SiO₂ catalystprovided in the Example below.

FIG. 4 shows an EXAFS spectra of the comparative Ni/SiO₂ catalystprovided in the Example below.

DETAILED DESCRIPTION

Certain terms are used throughout the following description and claimsto refer to particular components. As one skilled in the art willappreciate, various entities can refer to the same component bydifferent names, and as such, the naming convention for the elementsdescribed herein is not intended to limit the scope of the invention,unless otherwise specifically defined herein. Further, the namingconvention used herein is not intended to distinguish between componentsthat differ in name but not function. Furthermore, in the followingdiscussion and in the claims, the terms “including” and “comprising” areused in an open-ended fashion, and thus should be interpreted to mean“including, but not limited to.”

All numerical values in this disclosure can be exact or approximatevalues (“about”) unless otherwise specifically stated. Accordingly,various embodiments of the disclosure can deviate from the numbers,values, and ranges disclosed herein without departing from the intendedscope.

The term “or” is intended to encompass both exclusive and inclusivecases, i.e., “A or B” is intended to be synonymous with “at least one ofA and B,” unless otherwise expressly specified herein.

The indefinite articles “a” and “an” refer to both singular forms (i.e.,“one”) and plural referents (i.e., one or more) unless the contextclearly dictates otherwise.

The phrase “consisting essentially of” means that the described/claimedcomposition does not include any other components that will materiallyalter its properties by any more than 5% of that property, and in anycase, does not include any other component to a level greater than 3 wt%.

Each of the appended claims defines a separate invention, which forinfringement purposes is recognized as including equivalents to thevarious elements or limitations specified in the claims. Depending onthe context, all references to the “invention” may in some cases referto certain specific embodiments only. In other cases, it will berecognized that references to the “invention” will refer to subjectmatter recited in one or more, but not necessarily all, of the claims.Each of the inventions will now be described in greater detail below,including specific embodiments, versions and examples, but theinventions are not limited to these embodiments, versions or examples,which are included to enable a person having ordinary skill in the artto make and use the inventions, when the information in this disclosureis combined with publicly available information and technology.

A nickel-based catalyst useful for olefin oligomerization that retainsstability at high temperature is provided. It has been surprisingly anunexpectedly discovered that oligomerization can be achieved at highreaction temperatures using a nickel-based catalyst having a phosphateligand. With the presence of a phosphate ligand bonded to the nickelmetal center, the nickel surprisingly and unexpectedly remained in the+2 oxidation state at reaction temperatures at or above 500° C., andexhibited high stability and activity for light hydrocarbonoligomerization. Not wishing to be bound by theory, it is believed thatthe presence of a phosphate ligand on the nickel metal complex preventsor severely inhibits the reduction of Ni(II) to Ni(0) at reactiontemperatures at or above 500° C., allowing the oligomerization of lighthydrocarbons to higher molecular weight oligomers at much highertemperatures than could be achieved before.

By “oligomer(s)”, it is meant dimers, trimers, tetramers, and othermolecular complexes having less than 26 repeating units. Oligomersprovided herein are typically gases or liquids at ambient temperature,and can include low melting solids, including waxes, at ambienttemperature. In some embodiments, the oligomers provided herein can havean atomic weight or molecular weight of less than 10,000 AMU (Da), suchas about 5,000 or less, 1,000 or less, 500 or less, 400 or less, 300 orless, or 200 or less. The molecular weight of the oligomer, for example,can range from a low of about 50, 250 or 350 to a high of about 500,3,000, 7,000, or 9,000 AMU (Da).

The nickel-based catalyst does not require a co-catalyst or activator tocreate a vacant coordination site that will coordinate, insert, andoligomerize the olefin(s). For the purposes of this specification, theterms “cocatalyst” and “activator” are used herein interchangeably andrefer to any compound, other than the reacting olefin, that can activatethe nickel-based catalyst by converting the neutral catalyst compound toa catalytically active catalyst compound cation. For example, thefollowing co-catalyst and/or activators are not required: alumoxanes,aluminum alkyls, ionizing activators, which may be neutral or ionic,alumoxane compounds, modified alumoxane compounds, and ionizing anionprecursor compounds that abstract one reactive, σ-bound, metal ligandmaking the metal complex cationic and providing a charge-balancingnoncoordinating or weakly coordinating anion.

The nickel-based catalyst can be deposited on, contacted with, bondedto, or incorporated within, adsorbed or absorbed in, or on, one or moresupports or carriers. The support material can be any suitable supportmaterial. For example, the support material can be a porous supportmaterial, such as inorganic oxides. Other support materials can includesilica, which may or may not be dehydrated, fumed silica, alumina,silica-alumina or mixtures thereof. Other supports include magnesia,titania, zirconia, montmorillonite, phyllosilicate, zeolites, clays andthe like. Other support materials can include nanocomposites, andaerogels. Combinations of these support materials can be used, forexample, silica-chromium, silica-alumina, silica-titania and the like.

Particular, non-limiting examples of more preferred catalyst supportsinclude: silicon dioxide, aluminum oxide, titanium dioxide, zeolites,silica-alumina, cerium dioxide, zirconium dioxide, magnesium oxide,silica pillared clays, metal modified silica, metal oxide modifiedsilica, metal oxide modified silica-pillared clays, silica-pillaredmicas, metal oxide modified silica-pillared micas, silica-pillaredtetrasilicic mica, silica-pillared tainiolite, and combinations thereof.Such supports are commercially available or prepared by techniques knownto those skilled in the catalysis art.

The nickel-based catalyst can contain nickel in any amount sufficient tomake the oligomer(s) described. For example, the amount of nickel can beabout 2 wt % to about 20 wt %, or about 2 wt % to about 10 wt %, orabout 2 wt % to about 8 wt %, or about 2 wt % to about 5 wt %, or about2 wt % to about 3 wt %, or about 2.4 wt %, or about 2.5 wt %, or about2.6 wt %, or about 2.7 wt %, or about 2.8 wt %, based on the totalweight of the catalyst.

The support material can have a surface area in the range of from about10 m²/g to about 700 m²/g, a pore volume in the range of from about 0.1cc/g to about 4.0 cc/g and an average particle size in the range of fromabout 5 μm to about 500 μm. More preferably, the support material canhave a surface area in the range of from about 50 m²/g to about 500m²/g, pore volume of from about 0.5 cc/g to about 3.5 cc/g and averageparticle size of from about 10 μm to about 200 μm. The surface area canrange from a low of about 50 m²/g, 150 m²/g, or 300 m²/g to a high ofabout 500 m²/g, 700 m²/g, or 900 m²/g. The surface area also can rangefrom a low of about 200 m²/g, 300 m²/g, or 400 m²/g to a high of about600 m²/g, 800 m²/g, or 1,000 m²/g. The average pore size of the supportmaterial can range of from about 10 Å to 1000 Å, about 50 Å to about 500Å, about 75 Å to about 350 Å, about 50 Å to about 300 Å, or about 75 Åto about 120 Å.

In another embodiment the support material can be one or more types ofsupport materials which may or may not be treated differently. Forexample, one could use two different silicas each having different porevolumes or calcined at different temperatures. Likewise, one could use asilica that had been treated with a scavenger or other additive and asilica that had not.

The nickel-based catalyst can convert light hydrocarbon alkenes tohigher molecular weight oligomers at high temperatures and suitableoligomerization pressures. The light hydrocarbons or hydrocarbon feedstream can be or can include natural gas, natural gas liquids, ormixtures of both. The hydrocarbon feed stream can be derived directlyfrom shale gas or other formations. The hydrocarbon feed stream can alsooriginate from a refinery, such as from a FCC, coker, steam cracker, andpyrolysis gasoline (pygas) as well as alkane dehydrogenation processes,for example, ethane, propane and butane dehydrogenation. The hydrocarbonfeed stream can also be or can include syngas and coal gas.

The hydrocarbon feed stream can be or can include one or more olefinshaving from about 2 to about 12 carbon atoms. The hydrocarbon feedstream can be or can include one or more linear alpha olefins, such asethene, propene, butenes, pentenes and/or hexenes. The process isespecially applicable to ethene and propene oligomerization for makingC4 to about C26 oligomers.

The hydrocarbon feed stream can contain greater than about 65 wt %olefins, such as greater than about 70 wt. % olefins or greater thanabout 75 wt % olefins. For example, the hydrocarbon feed stream cancontain one or more C2 to C12 olefins in amounts ranging from a low ofabout 50 wt %, 60 wt % or 65 wt % to a high of about 70 wt %, 85 wt % or100 wt %, based on the total weight of the feed stream. The hydrocarbonfeed stream also can include up to 80 mol % alkanes, for example,methane, ethane, propane, butane, and pentane; although the alkanegenerally comprises less than about 50 mol % of the hydrocarbon feedstream, and preferably less than about 20 mol % of the hydrocarbonstream.

The hydrocarbon feed can have a temperature of 250° C. or higher. Forexample, the temperature of the hydrocarbon feed can range from a low ofabout 250°, 450° C., or 500° to a high of about 550° C., 600° C., or700° C. The temperature of the hydrocarbon feed also can be 420° C. orhigher, 450° C. or higher, 480° C. or higher, 500° C. or higher, 525° C.or higher, 550° C. or higher, 560° C. or higher, 570° C. or higher, or575° C. or higher, or 600° C. or higher.

The resulting oligomer(s) can be or can include one or more olefinshaving from 4 to 26 carbon atoms, such as 12 to 20 carbon atoms, or 16to 20 carbon atoms. The resulting oligomers, for example, can includebutene, hexene, octene, decene, dodecene, tetradecane, hexadecane,octadecene and eicosene and higher olefins, as well as any combinationsthereof. The resulting oligomer(s) also can have less than about 5%aromatics and less than about 10 ppm sulfur. The resulting oligomer(s)also can have zero or substantially no aromatics and zero orsubstantially no sulfur.

The resulting oligomer(s) are useful as precursors, feedstocks, monomersand/or comonomers for various commercial and industrial uses includingpolymers, plastics, rubbers, elastomers, as well as chemicals. Forexample, these resulting oligomer(s) are also useful for makingpolybutene-1, polyethylene, polypropylene, polyalpha olefins, blockcopolymers, detergents, alcohols, surfactants, oilfield chemicals,solvents, lubricants, plasticizers, alkyl amines, alkyl succinicanhydrides, waxes, and many other specialty chemicals.

The resulting oligomer(s) are especially useful for production of dieseland jet fuels, or as a fuel additive. In certain embodiments, theresulting oligomer(s) can have a boiling point in the range of 170° C.to 360° C. and more particularly 200° C. to 300° C. The resultingoligomer(s) also can have a Cetane Index (CI) of 40 to 100 and moreparticularly 65 to 100. The resulting oligomer(s) also can have a pourpoint of −50° C. or −40° C.

As mentioned above, it has been surprisingly an unexpectedly discoveredthat the nickel-based catalyst described herein can oligomerize lightalkene hydrocarbons to higher molecular weight oligomers at reactiontemperatures never thought possible. Suitable reaction temperatures canexceed 500° C., such as about 525° C., 550° C., and 600° C. The reactiontemperature, for example, can range from about 500° C. to about 600° C.or higher. Of course, lower reaction temperatures are also possible,such as between about 135° C., 200° C. or 225° C. and about 350° C.,400° C., or 500° C. Another significant advantage is that conventionaloligomerization pressures can be used. For example, the reactionpressure can range from about 400 psig to about 4000 psig (27.5 Bar to276 Bar), or about 500 psig to about 1500 psig (34.5 Bar to 103 Bar).The reaction pressure can also range from a low of about 400 psig (27.5Bar), 500 psig (34.5 Bar) or 600 psig (41.4 Bar) to a high of about1,000 psig (68.9 Bar), 1,200 psig (82.7 Bar), or 2,000 psig (138 Bar).

The oligomerization process can be carried out using any conventionaltechnique. The process can be carried out, for example, in a continuousstirred tank reactor, batch reactor or plug flow reactor. One or morereactors operated in series or parallel can be used. The process can beoperated at partial conversion to control the molecular weight of theproduct and unconverted olefins can be recycled for higher yields.Further, once the catalyst is deactivated with high molecular weightcarbon, or coke, it can be regenerated using known techniques in theart, including for example, by combustion in air at a temperature ofabout 400° C. or higher.

EXAMPLES

The foregoing discussion can be further described with reference to thefollowing non-limiting examples, which compare the stability andeffectiveness of an inventive nickel-phosphate catalyst to a conventionnickel oxide supported catalyst.

The comparative Ni/SiO₂ (nickel on silica) catalyst was prepared bydissolving 15.00 g of Ni (NO₃)₂.6H₂O (nickel nitrate hexahydrate) in 100mL of deionized (DI) water followed by the addition of 25.0 mL ofconcentrated NH₄OH (ammonium hydroxide). A clear blue solution wasobtained with a pH of 11. Then 50.0 g of SiO₂ (Davisil Grade 636, poresize 60 Á, 35-60 mesh, surface area 480 m²/g) was added to the solutionand the obtained suspension was stirred at room temperature for 20 mins.An additional 5.0 mL of NH₄OH was added to maintain the pH at 11 at theend of the reaction. It was stirred at room temperature for anadditional 10 mins before filtration and thorough washing with DI water.The obtained nickel (Ni)-adsorbed SiO₂ was dried at 125° C. overnightand calcined at 300° C. for 30 mins (5° C. per minute ramp to 300° C.).The Ni loading as determined by Atomic Adsorption Spectroscopy (AAS) was2.7 wt %.

The inventive Ni—P/SiO₂ (nickel phosphate on silica) catalyst wasprepared by diluting 0.4174 g of H₃PO₄ (phosphoric acid) (85% aq.) with3.5 mL of de-ionized (DI) water. This solution was then impregnated with5.0 g of the Ni/SiO₂ that was prepared as described above. Theimpregnated solution was calcinated in air at 600° C. (5° C. per minuteramp to 600° C.) for 1 hour and the Ni—P/SiO₂ was obtained (Scheme 1).The Ni loading as determined by AAS was 2.6 wt %.

The ethylene oligomerization catalytic performance testing was conductedin a vertical, 10.5 mm ID quartz tube reactor equipped with mass flowcontrollers. The catalyst was supported on quartz wool with an internalthermocouple monitoring the temperature of the catalyst bed. Theoligomerization products were products being monitored by a HP6890series Gas Chromatograph (GC) system with Agilent J&W HP-1 GC Column.

Example 1

The Ni—P/SiO₂ catalyst was purged with ultra-high purity nitrogen toremove any adsorbed moisture. It was then heated to a range oftemperatures from 200 to 580° C. to see if it was active at any of thesetemperatures, by introducing ethylene into the reactor and monitoringproducts through the GC system. A sample of Ni—P/SiO₂ catalyst (0.1 gcatalyst, 0.9 g silica) and 5% ethylene (balance nitrogen) at a flowrate of 25 ccm (cubic centimeter per minute) was used at atmosphericpressure for these tests. Oligomerization products started to appear attemperatures above 500° C.

Example 2

A fresh sample of catalyst (0.2 g catalyst, 0.8 g silica) was loadedinto the reactor and heated to 500° C. Then 25 ccm of 5% ethylene wasintroduced into the reactor at atmospheric pressure. Products weremonitored at 12-minute intervals through the GC system.

Example 3

A fresh sample of the same catalyst was heated in nitrogen to 500° C.and then pretreated with 99% hydrogen at this temperature for 30minutes. Ethylene was introduced into the reactor and the productsmonitored through the GC system.

Example 4

A fresh sample of the same catalyst was heated to 500° C. in nitrogenand 25 ccm of 5% ethylene and 5 ccm of 99% hydrogen were co-fed into thereactor. The same series of tests were repeated at 550° C. with onedifference, the catalyst loading was 0.5 g catalyst and 0.5 g silica(Table I). To compare with the Ni—P/SiO₂ catalyst, the same series oftests as above were performed for the Ni/SiO₂ (0.5 g) catalyst. Nocatalytic activity/products were observed at any of these conditions.The Ni/SiO₂ catalyst was not active at these elevated temperatures.

TABLE 1 OLIGOMERIZATION TESTS ON Ni-P/SiO₂ Hydrogen Ethylene (99%)Selectivity for Catalyst Temperature Pressure Flow flow ConversionButene loading (° C.) (atm) (ccm) (ccm) (%) (%) EXAMPLE 2: Reaction in5% Ethylene in Nitrogen Ni-P/SiO₂ 500 1 25 — 0.28 100 (0.2 g) Ni-P/SiO₂550 1 25 — 0.63  80 (0.5 g) EXAMPLE 3: Reaction in 5% Ethylene inNitrogen and co-feeding with 99% Hydrogen Ni-P/SiO₂ 500 1 25 5 0.15 100(0.2 g) Ni-P/SiO₂ 550 1 25 5 0.4   78 (0.5 g) EXAMPLE 4: Reaction in 5%Ethylene in Nitrogen after pretreatment with 99% Hydrogen for 30 minutesNi-P/SiO₂ 500 1 25 — 0.13 100 (0.2 g) Ni-P/SiO₂ 550 1 25 — 0.35  79 (0.5g)

The presence of hydrogen co-feed decreased the conversion of theNi—P/SiO₂ due to reduction in partial pressure of ethylene. TheNi—P/SiO₂ catalyst was tested at 550° C. in ethylene for 6 hours withoutany deactivation. Only even carbon numbered components, up to hexenes,were detected in which butenes were the main products. The active nickelsites mainly dimerized ethene to butene while only a limited amount ofbutene further reacted toward hexene. The selectivity towards butene,and hexene amounted to 80%, and 20% respectively.

The Ni—P/SiO₂ and the Ni/SiO₂ catalysts were examined on the advancedphoton source (APS) beamline facility at Argonne national lab (ANL).Spectroscopic data collection for Extended X-ray Absorption FineStructure (EXAFS) and X-ray Absorption Near-Edge Structure (XANES) wascarried out at ambient and reaction conditions of (500° C. and 550° C.)with and without the presence of hydrogen. Catalyst samples (˜10 mg)were pressed into a cylindrical sample holder consisting of six wells,forming a self-supporting wafer to prepare for this test.

It was observed in the in-situ XANES (FIG. 1) for the Ni—P/SiO₂ catalystthat under reaction conditions, after introduction of ethylene forfifteen minutes, the Ni(II) was stable at 500° C. and even afterco-feeding with hydrogen for fifteen minutes at 550° C., the Ni (II)showed no signs of reduction. The spectra are indistinguishable fromeach other, which implies stable tetrahedral geometry of Ni(II) and +2oxidation state of Ni under reaction conditions.

It can also be seen from the XANES for Ni/SiO₂ (FIG. 2), there was aslight change in edge peak height at 500° C. in presence of ethylene andat 550° C. a bigger change was observed. The change in edge peak heightsignifies a decrease in the number of Ni (II) atoms. The pre-edge almostdisappears at 550° C. indicating loss of tetrahedral coordinated Ni (II)and reduction to Ni (0). The leading edge energy of the XANES afterreaction (8333.0 eV) is identical to that of metallic Ni foil,indicating the reduction of Ni (II) to metallic Ni nanoparticles.

The XANES data were fit to find the fraction of each oxidation state ofnickel in both catalyst samples at ambient and reaction conditions. Nifoil was taken as reference for the Ni (0) to determine the percentageof reduced Ni in both catalyst samples as calculated in the Table II.

TABLE II XANES DATA Edge Pre-edge energy energy Oxidation SampleTreatment (eV) (eV) state Ni-P/ 500° C., air 8342.8 8333.0 Ni(II) SiO₂Measured at 550° C. 500° C., H₂ + C₂H₄ 8342.8 8333.0 Ni(II) Measured at550° C. 500° C., C₂H₄ 8342.8 8333.0 Ni(II) Measured at 550° C. Ni/ 500°C., air 8342.2 8333.0 Ni(II) SiO₂ Measured at 550° C. 500° C., C₂H₄8342.2 8333.0  5.9% Ni(0) + Measured at 550° C. (pre-edge) 94.1% Ni(II)550° C., C₂H₄ 8333.0 — 34.1% Ni(0) + Measured at 550° C. 65.9% Ni(II)550° C., C₂H₄ + H₂ 8333.0 — 63.9% Ni(II) + Measured at 550° C. 36.1%Ni(0) Ni RT 8333.0 — Ni(0) foil

The EXAFS spectra was useful in determining the distances between Ni andthe neighboring atoms, as well as the coordination number and thecomposition of the surrounding atoms. As can be seen in FIG. 3, thepeaks were almost similar for Ni—P/SiO₂ EXAFS at all conditions. Theslight changes in the EXAFS spectra are due to the background noise.

As can be seen from the Ni/SiO₂ EXAFS (FIG. 4), there was a decrease inpeak height at −1.5 Å that indicates the loss of Ni—O bonds.Additionally, the changes of the peak at −2.5 Å was a sign of theformation of Ni—Ni scattering, which is direct evidence of reduction ofNi (II) to Ni (0). The EXAFS data were fit as detailed in Table IIIbelow.

TABLE III EXAFS FITTING RESULTS Sample Treatment S₀ ² C. N. E₀ (eV) R(Å) Sigma² Ni-P/SiO₂ 500° C., air 1.0 4.0 -7.6 1.97 0.015 Measured at500° C. 500° C., H₂ + C₂H₄ Measured at 500° C. 500° C., C.₂H₄ Measuredat 500° C. k-range: 3.0-11.0 Å⁻¹; R-range: 1.0-2.0 Å; R-factor: k¹:0.0003; k²: 0.0013; k³: 0.0063 Ni-P/SiO₂ 500° C., air 1.0 4.4 −5.3 2.000.010 Measured at RT k-range: 3.0-11.0 Å⁻¹; R-range: 1.0-2.0 Å;R-factor: k¹: 0.0003; k²: 0.0010; k³: 0.0038 Ni/SiO₂ 500° C., air 1.04.6 −2.7 2.04 0.008 Measured at RT k-range: 3.0-11.0 Å⁻¹; R-range:1.0-2.0 Å; R-factor: k¹: 0.0010; k²: 0.0016; k³: 0.0032 Ni/SiO₂ 500° C.,air 1.0 4.4 −4.7 2.01 0.013 Measured at 500° C. k-range: 3.0-11.0 Å⁻¹;R-range: 1.0-2.0 Å; R-factor: k¹: 0.0012; k²: 0.0027; k³: 0.0085 Ni/SiO₂500° C., C.₂H₄ 1.0 3.7 −4.3 2.00 0.011 Measured at 500° C. k-range:3.0-11.0 Å⁻¹; R-range: 1.0-2.0 Å; R-factor: k¹: 0.0012; k²: 0.0027; k³:0.0085 Ni/SiO₂ 550° C., C₂H₄ 1.0 1.8 −5.1 1.97 0.011 Measured at 550° C.k-range: 3.0-11.0 Å⁻¹; R-range: 1.0-2.0 Å; R-factor: k¹: 0.0012; k²:0.0027; k³: 0.0085 Ni/SiO₂ 550° C., C₂H₄ + H₂ 1.0 1.3 −4.7 1.97 0.002Measured at 550° C. k-range: 3.0-11.0 Å⁻¹; R-range: 1.0-2.0 Å; R-factor:k¹: 0.0012; k²: 0.0027; k³: 0.0085

From the XANES and EXAFS, the Ni—P/SiO₂ was stable in the presence ofethylene as well as hydrogen at higher temperature (500-550° C.) and didnot show any sign of reduction to metallic Ni(0).

In case of the comparative Ni/SiO₂ catalyst, the shift of the EXAFSspectrum to lower energy indicated the reduction of Ni (II) to Ni (0).These changes also indicated a loss in the Ni—O coordination andincrease of the Ni—Ni coordination, which is consistent with thereduction of Ni (II) ions and formation of Ni (0) nanoparticles. At 550°C., in presence of ethylene and hydrogen for fifteen minutes, the Ni(II) percentage fell to 65.9% Ni (II) (Table II), which shows theinstability of Ni (II) on silica catalysts. Its coordination number alsodecreased from 4.6 to 1.3 (Table III) indicating a loss of tetrahedralgeometry.

Based on the results and findings above, it has been surprisingly andunexpectedly discovered that Ni—OP bonds are more resistant to hydrogenreduction, and prevent Ni(II) ions from reducing at temperatures above500° C. It was more surprising and unexpected that the Ni—P/SiO₂catalyst was active at temperatures above 500° C. While the currentresults showed a low conversion, it is believed that increasing thepressure would increase the rate of reaction, but is unlikely to changethe oxidation sate of Ni(II). In contrast, the comparison catalystNi/SiO₂ did not show any ethylene oligomerization at temperatures above500° C.

Features of the present invention further relate to any one or more ofthe following embodiments.

1. An oligomerization catalyst comprising a nickel phosphate compoundand a support.

2. The catalyst according to embodiment 1, wherein the nickel has a +2oxidation state at a temperature of 650° C. or higher.

3. The catalyst according to embodiments 1 or 2, wherein phosphoric acidis a source for the phosphate.

4. The catalyst according to any embodiment 1 to 3, wherein nickelnitrate hexahydrate is a source for the nickel, and the nickel ispresent in an amount ranging from about 2 wt % to about 20 wt %, basedon the total weight of the catalyst.

5. The catalyst according to any embodiment 1 to 4, wherein the supporthas a surface area of about 100 m²/g to about 600 m²/g.

6. The catalyst according to any embodiment 1 to 5, wherein the supporthas a pore size of about 50 Å to about 500 Å.

7. The catalyst according to any embodiment 1 to 6, wherein the supportis silica oxide, aluminum oxide or silica-aluminum oxide.

8. A method for making a nickel phosphate catalyst, comprising:providing a solution of a nickel hydrate and a Lewis base; adding asupport material to the solution to provide a supported nickel catalyst;calcining the supported nickel catalyst; mixing a phosphate with thesupported nickel catalyst to form an impregnating solution containingnickel phosphate; and calcining the impregnating solution to obtain asupported nickel phosphate catalyst.

9. The method according to embodiment 8, wherein the Lewis base isammonium hydroxide.

10. The method according to embodiments 8 or 9, wherein the supportmaterial has a pore size of about 50 Å to about 500 Å, and a surfacearea of about 100 m²/g to about 600 m²/g.

11. The method according to any embodiment 8 to 10, wherein the nickelof the nickel phosphate catalyst has a +2 oxidation state at atemperature of 500° C. or higher.

12. The method according to any embodiment 8 to 11, wherein phosphoricacid is a source for the phosphate.

13. The method according to any embodiment 8 to 12, wherein thesupported nickel catalyst is calcined using air at a temperature ofabout 200° C. to about 400° C.

14. The method according to any embodiment 8 to 13, wherein the solutionof the nickel hydrate and Lewis base has a pH of about 10 to about 12.

15. A method for making light hydrocarbon oligomers, comprising:reacting one or more C2 to C12 olefins with a supported nickel phosphatecatalyst at a temperature of about 500° C. or higher to provide anoligomer product comprising C4 to C26 olefins, wherein the nickel ispresent in an amount ranging from about 2 wt % to about 20 wt %, orabout 2 wt % to about 10 wt %, or about 2 wt % to about 8 wt %, or about2 wt % to about 5 wt %, based on the total weight of the catalyst.

16. The method according to embodiment 15, wherein the support materialis silica having a pore size of about 50 Á to about 500 Á, and a surfacearea of about 100 m²/g to about 600 m²/g.

17. The method according to embodiments 15 or 16, wherein the one ormore C2 to C12 olefins and the supported nickel phosphate catalyst arereacted at a pressure of about 6.8 Bar(g) to about 138 Bar(g).

18. The method according to any embodiment 15 to 17, wherein the one ormore C2 to C12 olefins consist essentially of ethylene and propylene.

19. The method according to any embodiment 15 to 18, wherein theoligomer product consists essentially of C4 to C26 olefins.

20. The method according to any embodiment 15 to 19, wherein theoligomer product consists essentially of C12 to C20 olefins having aboiling point in the range of 170° C. to 360° C.

Certain embodiments and features have been described using a set ofnumerical upper limits and a set of numerical lower limits. It should beappreciated that ranges from any lower limit to any upper limit arecontemplated unless otherwise indicated. Certain lower limits, upperlimits and ranges appear in one or more claims below. All numericalvalues are “about” or “approximately” the indicated value, and take intoaccount experimental error and variations that would be expected by aperson having ordinary skill in the art.

Various terms have been defined above. To the extent a term used in aclaim is not defined above, it should be given the broadest definitionpersons in the pertinent art have given that term as reflected in atleast one printed publication or issued patent. Furthermore, allpatents, test procedures, and other documents cited in this applicationare fully incorporated by reference to the extent such disclosure is notinconsistent with this application and for all jurisdictions in whichsuch incorporation is permitted.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for making a nickel phosphate catalyst,comprising: providing a solution of a nickel hydrate and a Lewis base;adding a support material to the solution to provide a supported nickelcatalyst; calcining the supported nickel catalyst; mixing a phosphatewith the supported nickel catalyst to form an impregnating solutioncontaining nickel phosphate; and calcining the impregnating solution toobtain a supported nickel phosphate catalyst.
 2. The method of claim 1,wherein the Lewis base is ammonium hydroxide.
 3. The method of claim 1,wherein the support material has a pore size of about 50 Å to about 500Å, and a surface area of about 100 m²/g to about 600 m²/g.
 4. The methodof claim 1, wherein the nickel of the nickel phosphate catalyst has a +2oxidation state at a temperature of 500° C. or higher.
 5. The method ofclaim 1, wherein phosphoric acid is a source for the phosphate.
 6. Themethod of claim 1, wherein the supported nickel catalyst is calcinedusing air at a temperature of about 200° C. to about 400° C.
 7. Themethod of claim 1, wherein the solution of the nickel hydrate and Lewisbase has a pH of about 10 to about 12.